sex in bacteria Flashcards
how do bacteria have “sex”
they exchange DNA either through horizontal or lateral gene transfer
transduction: bacteria infected with virus may pick up pieces of bacterial DNA, this virus may spread to other bacteria carrying DNA with it and spreads bacterial DNA and encorporates it
conjugation: plasmids are small circular pieces of DNA, these are transferable between bacteria, they are a selfish genetic element
transformation: cells have ability to pick up naked DNA from environment, bacteria may pick up DNA from other dead bacteria who release DNA into envrionment
what genes do plasmids carry, and how do plasmids relate to fitness
bacterial core genome is 2,000 genes, “house keeping genes”
plus 3,000-5,000 non core genes drawn from pan genome of non essential 18,000 genes
plasmids only contain non core genes, they may carry;
selfish genes; for replication, conjugation incompatibility genes that exclude other plasmids
beneficial genes; antibiotic resistance, enzymes, detoxification agents (e.g ecologically specialised genes)
social genes: that benefit or harm neighbours such as bacteriocins that harm non related neighbour
plasmid production may reduce the individuals fitness; a study done on yeast which contain plasmids showed increased plasmid copy number was associated with decreased fitness, however selection retains plasmids, in a study of pseudomonas fluorescens bacteria the pQRB plasmid confers mercury resistance, different colonies were treated with mercury at different frequencies, in colonies with no treatment the plasmid was lost very quickly, ones treated frequently maintain plasmid even after mercury treatment stops, in pseudomonas putida ones treated with mercury the plasmid is integrated into the bacterial chromosome
what is the mechanism for selfish plasmids
they use a R-M (restriction modification system) on R1 plasmid which leads to post segregational killing
R enzyme cuts DNA at particular sites, M methylates cytosines in DNA and protects these sites, R has longer half life than M
meaning that if plasmid is lost then M breaks down longer than R and so bacterium without plasmid dies, giving owner the advantage, meaning it is an essential plasmid, they may also be used to kill non related competitors, can also be integrated on bacterial chromosome
describe transformation
may allow cross species transfer of DNA
involves the active uptake of self DNA, in gram negative bacteria DNA fragments cannot easily cross, there is a recognition sequence, in haemophilus influenzae it is 9bp, this recognition sequence makes uptake 10-100 times more efficient than random sequences
what are benefits of transformation
repair DNA damage (in double strand damage) however would require bacteria to be lucky in picking up right DNA
recombination: creating variation allow adaptation
uptake of new genes may allow traits increasing fitness
gene loss; allows removal of unnesscary DNA being more efficient
random mobile elements with marker inserted into salmonella and removed, destroying nearby DNA, at some locations this was proved to be beneficial since loss of unnessecary DNA
food: DNA is taken up and degraded and nucleotides are used
